1. Field of the Invention
The present invention relates to a fuel nozzle for gas turbines engines and, more particularly, to a fuel nozzle stem through which distinct fuel conduits can be defined.
2. Description of the Prior Art
Fuel nozzles for gas turbine engines are well known in the prior art. Such conventional fuel nozzles are used to supply fuel to a combustion chamber which is provided for igniting the fuel mixture, thereby producing the energy which is used to power the engine. Generally, the combustion chamber includes a plurality of fuel nozzles to thus ensure a proper distribution of the fuel mixture within the combustion chamber.
Conventional fuel nozzles include an inlet housing which is coupled to a fuel injector, a stem portion which defines dual fuel passages and at least one tip assembly of the nozzle for spraying or atomizing fuel into the combustion chamber. More particularly, the stem portion of such fuel nozzles consists of a primary tube and a secondary tube which are disposed within an outer tube which is adapted to provide structural support and thermal insulation to the tubing assembly. Indeed, the outer tube is exposed to hot compressor discharge air and thus some spacers are required to protect the inner tubes, i.e., the primary and secondary tubes, from contact with the hot outer tube.
Typically, the primary tube and the secondary tube are concentrically disposed within the outer tube so as to define two distinct conduits for directing primary and secondary fuel flows respectively. More particularly, the primary fuel is conveyed through a conduit of circular cross-section defined by the primary tube while the secondary fuel is delivered through the annular space defined between the primary and the secondary tube.
According to another configuration of the above fuel nozzle, the primary and the secondary tubes are not concentrically disposed within the outer tube, and thus the secondary fuel flows through the circular conduit of the secondary tube instead of passing through the annular space which is comprised between the primary and secondary tubes of the previous concentric structure. U.S. Pat. No. 4,735,044, issued on Apr. 5, 1988 to Richey et al, and U.S. Pat. Nos. 5,423,178 and 5,570,580, respectively issued on Jun. 13, 1995 and Nov. 5, 1996 to Mains, disclose such a dual stem for a gas turbine fuel nozzle.
U.S. Pat. No. 3,684,186, issued on Aug. 15, 1972 to Helmrich, and U.S. Pat. No. 4,609,150, issued on Sep. 2, 1986 to Pane, Jr. et al, teach having fuel and air passages which extend through a single element. More particularly, U.S. Pat. No. 3,684,186 discloses an aerating fuel nozzle which comprises a primary fuel passage, a secondary fuel passage and a plurality of circumferentially spaced air passages, all these passages being drilled through the main support structure of the fuel nozzle or defined by the space that exists between some adjacent components of the aerating fuel nozzle. U.S. Pat. No. 4,609,150 discloses a fuel nozzle which is cast into two distinct portions, one being the main support structure and the other being the nozzle head. More particularly, a fuel passage and an air passage are cast into the main support structure, and the nozzle head is provided with air swirler vanes, a frusto-conical air passage and a fuel swirl orifice plate. The head portion is welded to the end of the nozzle support portion so as to form an integral fuel nozzle.